development of a virtual simulator for planning mandible ... · govea-valladares y cols....

NOTA TECNICA

Vol. 33, Num. 2, Diciembre, 2012, pp. 147-158

Development of a Virtual Simulator for Planning

Mandible Osteotomies in Orthognathic Surgeries

E.H. Govea-Valladares ∗

H.I. Medellın-Castillo ∗

T. Lim∗∗

B. Khambay ∗∗∗

M. Rodrıguez-Florido∗∗∗∗

J. Ballesteros ∗∗∗∗

∗Facultad de Ingenierıa,

Universidad Autonoma de

San Luis Potosı, S.L.P.

Mexico.∗∗Innovative

Manufacturing Research

Centre, Heriot-Watt

University, Edinburgh,

UK.∗∗∗Dental School,

University of Glasgow,

Glasgow, UK.∗∗∗∗Instituto Tecnologico

de Canarias, Las Palmas,

Islas Canarias, Espana.

ABSTRACT

Surgery knowledge and training is typically transmitted by the teacher-

student method. In particular, the training process is carried out during real

surgical interventions and under supervision of an experienced surgeon. Recent

advancements in computer interaction technology and virtual environments

allow a wide variety of surgical procedures to be simulated. Virtual reality (VR)

applications range from art to engineering, science and medicine. In medicine,

virtual simulators are being developed for pre-operative planning and training

purposes. In this way, the transferring process of surgery knowledge and training

can be enhanced and speed up. Medical VR simulators are characterized by

their large demands on visual and physical behavior, and more recently the

demand for the sense of touch, which is an essential aspect in surgery. Regarding

the maxillofacial surgery, one of the most common surgical procedures is the

‘Bilateral Sagittal Split Ramus Osteotomy Mandibular” (BSSROM), which is

used to relocate the jaw at the correct position, fix jaw deformities, get better

functionality of the jaw and improve the patient aesthetic. In this paper the

development of a 3D virtual simulator for planning mandible osteotomies in

orthognathic surgeries is presented; in particular the work is focused on the

BSSROM procedure. The proposed system has been developed in an open-

source platform that provides a high level of realism and interaction, and where

the surgeons are able to cut bone in a 3D free-form way; thus enhancing the

traditional virtual osteotomy approach which is based on cutting planes. Some

of the main functionalities of the system include: virtual reality environment

and real-time response; 3D visualization of anatomical models and tools; free-

form manipulation and interaction of cutting tool, bone, and bone fragments;

simulation of single and multiple osteotomies; cutting planes osteotomies and

free-form cut osteotomies. The description, development and implementation

of the system are presented in this paper. The results have shown that the

proposed system is practical and can be used for planning and training mandible

osteotomies.

Keywords: virtual simulator, surgical planning, BSSROM, osteotomies, jaw.

148 Revista Mexicana de Ingenierıa Biomedica · volumen 33 · numero 2 · Diciembre, 2012

Correspondencia:E.H. Govea-Valladares

Av. Dr. Manuel Nava #8Edificio P Zona

Universitaria, CP 78290 SanLuis Potosı, S.L.P. Mexico,

Tel/fax (444) 8-17-33-81Correo electronico:

[email protected]

Fecha de recepcion:31/Octubre/2012

Fecha de aceptacion:

27/Noviembre/2012

RESUMEN

El conocimiento y entrenamiento quirurgico normalmente se transmite por el

metodo maestro-alumno. En particular, el proceso de entrenamiento se lleva a

cabo durante las intervenciones quirurgicas reales y bajo la supervision de un

cirujano experimentado. Los recientes avances en la tecnologıa computacional y

la interaccion con entornos virtuales han permitido que una amplia variedad de

intervenciones quirurgicas puedan ser simuladas. Las aplicaciones de la realidad

virtual (VR) abarcan desde el arte hasta la ingenierıa, ciencia y medicina. En

medicina, los simuladores virtuales estan siendo desarrollados con propositos

de planeacion y entrenamiento pre-operatorio. De esta manera el proceso de

transferencia de conocimiento y entrenamiento quirurgico puede mejorarse y

acelerarse. Los simuladores medicos de realidad virtual se caracterizan por

sus grandes demandas visuales y comportamiento fısico, y mas recientemente

la demanda por el sentido del tacto, que es un aspecto esencial en la cirugıa.

Con respecto a la cirugıa maxilofacial, una de las procedimientos quirurgicos mas

comunes es la ‘Osteotomıa Sagital Bilateral de Rama Mandibular’ (OSBRM),

la cual se utiliza para relocalizar la mandıbula en la posicion correcta, corregir

deformidades de la mandıbula, conseguir un mejor funcionamiento de la

mandıbula y mejorar la estetica del paciente. En este artıculo se presenta el

desarrollo de un simulador virtual 3D para planeacion de cirugıas de osteotomıa

mandibular ortognatica, en particular este trabajo se enfoca en el procedimiento

OSBRM. El sistema propuesto ha sido desarrollado en una plataforma de codigo

abierto y ofrece un sistema mas realista e interactivo, en donde los cirujanos

pueden cortar hueso de una manera libre y en 3D, mejorando ası el enfoque

tradicional de la osteotomıa virtual basada en planos de corte. Algunas de las

funcionalidades principales del sistema son: un entorno de realidad virtual y

respuesta en tiempo real; visualizacion en 3D de biomodelos y herramientas;

interaccion y manipulacion libre de herramientas de corte, huesos y fragmentos

de huesos; simulacion de osteotomıas simples y multiples; osteotomıas con planos

de corte y de forma libre. La descripcion, el desarrollo y la aplicacion del sistema

se presentan en este documento. Los resultados han demostrado que el sistema

propuesto es practico y puede ser utilizado en la planeacion y entrenamiento de

osteotomıas mandibulares.

Palabras clave: simulador virtual, planificacion quirurgica, OSBRM, osteotomıas,

mandıbula.

INTRODUCTION

Virtual Reality (VR) is one of the mainareas of knowledge that have taken advantageof the computer technological development 1.It has been used in different applications

such as engineering, education, entertainment,astronomy, archaeology and medicine, amongmany other 2. In the area of medicine,virtual environments can be created to reproducedifferent scenarios that enable the interactionwith the human body anatomy 3.

Govea-Valladares y cols. Development of a virtual simulator for planning mandible osteotomies in orthognathic surgeries 149

The practice of medicine is performedthrough a teamwork and a complex decisionmaking process 4. Practitioner abilities inmedicine are gained by experience and training,which is a slow process and takes severalyears. To get experience and abilities, astudent of medicine must be the protagonist ofhis/her training, taking into account as a mainpriority the avoidance of risks and unnecessaryinconveniences for the patient 5. The useof VR in medicine may allow the student orpractitioner to understand and confirm conceptsand to improve skills in surgical practice, whileexperienced surgeons can plan or diagnostic withmore accuracy 6.

In general, a VR application in medicine iscomposed of three main modules:

1. 3D model reconstruction module, which isresponsible of generating 3D anatomicalmodels from medical data such as CT andMRI images.

2. 3D visualization module, which isresponsible of the graphics rendering ofthe virtual environment.

3. Manipulation module, needed to providethe interaction between the user and thevirtual environment 7.

The Bilateral Sagittal Split OsteotomyRamus Mandibular (BSSROM) procedure is acommon technique used for the correction offacial deformities in an individual; it allowsperforming mandibular movements in differentplanes 8. The BSSROM represents the mostcommonly used procedure orthognathic surgery9. Over the years, it has been graduallymodified in terms of design, extension andinstrumentation 10. These modifications makeit technically friendly, predictable, biologicallyacceptable and versatile.

This paper presents the development ofa VR system for planning and training ofmandible osteotomies in orthognathic surgeries.Currently the development has been focusedon the BSSROM procedure. The description,development and implementation of theproposed system are presented.

LITERATURE REVIEW

Several works related to the use of VR techniquesin surgery simulation, maxillofacial surgery andvirtual osteotomies, have been reported in theliterature. The following paragraphs summarizesome of these works.

Virtual maxillofacial surgery

Virtual surgery is an effective, definitive andobjective tool for reconstruction and correctionof facial deformities 11. The use of virtualsurgery enhances the diagnosis and treatmentplanning. It can also simulate the resultsafter performing surgery. In 12 the differencesbetween virtual and real surgical outcomes weremeasured using a voxel-wise rigid registration ofthe cranial base with construction of pre- andpost-surgery 3D models. The use of surgicaltemplates to perform mandible reconstructionsurgery according to the preoperative simulationwas presented in 13. The accuracy wasevaluated by means of cadaveric surgery in a3D environment. The reconstructed mandiblesshowed high similarity to the surgical planning interms of the mean translation, angular deviation,and rotation of segments of the reconstructedmandibles. A comparative analysis betweenthe surgical outcomes achieved with Computer-Aided Surgical Simulation (CASS) and thetraditional methods was presented in 14. A3D skull model of twelve consecutive patientswith Cranio Maxillofacial was generated. Thesemodels underwent 2 virtual surgeries: 1 wasbased on CASS (experimental group) and theother was based on traditional methods 1 yearlater (control group). The results showed thatthe surgical outcomes achieved with CASS aresignificantly better than those achieved withtraditional planning methods.

A computer imaging software that enablessurgeons to perform 3D virtual orthognathicsurgical planning was presented in 15. Thissoftware can provide a realistic and accurateforecast of the patient’s facial appearanceafter surgery. A new method for conductingmandibular model surgery, which provides animproved 3D assessment of the prescribed


mandibular yaw movements, was presented in16. A total of 670 students were evaluated inthe use of simulated patients in conjunction withanatomic and tissue task-training 17. The resultssuggested that the combination of simulatedpatients and simulation models yields to reliablescores for procedural and interpersonal skills.On the other hand, a virtual simulator toevaluate dental surgeries was presented in 18.A group of 53 dental students provided theirimpressions after virtual simulation. Theresults showed that 51 of the 53 studentsrecommended the virtual simulation as anadditional training modality in dental education.A new method to automatically compute themid-facial plane for planning cranio-maxillofacialinterventions based on 3-dimensional (3D)virtual models was presented in 18. Thestudy included experienced and inexperiencedclinicians defining the symmetry plane by aselection of landmarks; this manual definitionwas systematically compared with the definitionresulting from the new automatic method. Theresults showed that the new automatic method isreliable and leads to significantly higher accuracythan the manual method when performed byinexperienced clinicians.

A virtual reality tool for CASS, named‘The Hollowman’, was presented in 20. ‘TheHollowman’ was used in orthognatic surgeryto control the translocation of the maxillaafter Le Fort I osteotomy within a bimaxillaryprocedure. The tool was proved to bevery valuable especially in complex nonlineartranslocations of the maxilla because thesurgeon could directly visualise the positionof the mobilised bone in relation to thepreoperatively planned situation. The use andcombination of volumetric tomography and 3Ddental software programs, as tools for oral andmaxillofacial surgery, was discusses in 21. Theresults suggest that the combination of thesetechnologies is useful for expanding informationin dentoalveolar, preprosthetic, trauma,pathology and reconstruction, orthognathic,craniofacial, and surgical cases of estheticimplant. Moreover, the precision, accuracy, and3D visualization capabilities of these technologiesopen avenues for the oral and maxillofacial

surgeon in the diagnosis, planning, and surgicalmanagement. In 22 it was presented a studyto examine 3D virtual anatomical features ofthe sphenoid sinus and adjacent structuresduring virtual surgery, and to explore theirrelevance to actual transsphenoidal surgery. Thestudy primarily focused on performing a virtualsurgery to get measures and data needed inthe real surgery. The study provided virtualanatomical information about the sphenoid sinusand important surrounding structures, which isessential for a successful real life transsphenoidalsurgery.

Virtual osteotomies

The use of computer-assisted three-dimensionalsurgical planning in condylar reconstructionby vertical ramus osteotomy was described in23. The results showed that the combinationbetween surgical planning system and simulationmakes the surgery more accurate and convenient,and avoids damage to vital structures. Onthe other hand, the amount of interferencebetween the mandible proximal and distalsegments generated by 3 different osteotomymethods using computer simulation was assessedin 24. They demonstrated no difference insevere prognathism and asymmetry cases. In 25the surgical outcomes in free fibula mandibularreconstructions planned with virtual surgerywere evaluated. From a total of 19 mandibularosteotomies, the results showed that virtualsurgical planning have a positive impact onaccuracy because it is possible to get moreaccurate measurements than manually, even bythe hands of experienced surgeons.

Some virtual tools have been designed toassist the sagittal split osteotomy, after or beforeof the surgical procedure. In 26 the course ofthe mandibular canal at three positions usingcomputed tomography (CT) was evaluated. Therisk of injury to the inferior alveolar nervein classical sagittal split osteotomy, based onthe proximity of the mandibular canal tothe external cortical bone, was assessed andalternative surgical techniques using computer-assisted surgery were proposed. The use of3D finite element analysis to compare the


biomechanical stability of bilateral sagittal splitramus osteotomies fixed by lag screws with linearand triangular configuration was presented in27. Posterior occlusal loads were simulated tocalculate the stress fields on both the segmentsand the fixing appliances by the MSC Marcsoftware.

From the literature, it can be observed thatvirtual reality in medical applications has beenwidely used. Most of the surgical simulatorshave been designed for specific applications andthey are based on a traditional manipulation ofvirtual models using the 2D mouse. On the otherhand, virtual osteotomy simulators are basedon cutting planes defined by the user, which isfar from real osteotomy procedures where thebone is cut manually and the hand accuracyof the specialist is important. Thus, in thispaper the development of a virtual osteotomysimulator is proposed in order to enhance thetraditional virtual osteotomy approach based oncutting planes and 2D interaction. The proposedsystem provides a more realistic and interactivesystem where the surgeons are able to cut bonein a 3D free-form way. Also the system allowsthe free 3D manipulation of tools and anatomicalmodels.

BSSROM PROCEDURE

The Bilateral Sagittal Split Osteotomy RamusMandibular (BSSROM) procedure starts withthe cutting of the internal wall in the upper partof the ascending ramus of the mandible 28. Themark that leaves the tool serves as a guide to sawthe rest of the jawbone 29. Figure 1 shows thisprocedure 29.

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interactive system where the surgeons are able to cut bone in a 3D free-form way. Also the system allows the free 3D

manipulation of tools and anatomical models.

3. BSSROM PROCEDURE

The Bilateral Sagittal Split Osteotomy Ramus Mandibular (BSSROM) procedure starts with the cutting of the internal wall in

the upper part of the ascending ramus of the mandible 28. The mark that leaves the tool serves as a guide to saw the rest of

the jawbone 29. Figure 1 shows this procedure 29.

Figure 1: Cutting with the mill 29.

The next cut is performed following an oblique path from top to bottom and using a saw 10. The saw leaves a line mark as

showed in Figure 2. The surgeon can then change the direction of the saw to cut only about 5 mm from the bottom edge 31.

Figure 2:.Cutting with the sagittal saw 29.

The manual separation of the bone fragments is then carried out by pushing downwards and doing lateral movements along

the ramus 10. The last step is to set both parts with mini plates and screws of titanium 10, 31, Figure 3.

Fig. 1. Cutting with the mill 29.

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interactive system where the surgeons are able to cut bone in a 3D free-form way. Also the system allows the free 3D

manipulation of tools and anatomical models.

3. BSSROM PROCEDURE

The Bilateral Sagittal Split Osteotomy Ramus Mandibular (BSSROM) procedure starts with the cutting of the internal wall in

the upper part of the ascending ramus of the mandible 28. The mark that leaves the tool serves as a guide to saw the rest of

the jawbone 29. Figure 1 shows this procedure 29.

Figure 1: Cutting with the mill 29.

The next cut is performed following an oblique path from top to bottom and using a saw 10. The saw leaves a line mark as

showed in Figure 2. The surgeon can then change the direction of the saw to cut only about 5 mm from the bottom edge 31.

Figure 2:.Cutting with the sagittal saw 29.

The manual separation of the bone fragments is then carried out by pushing downwards and doing lateral movements along

the ramus 10. The last step is to set both parts with mini plates and screws of titanium 10, 31, Figure 3.

Fig. 2. Cutting with the sagittal saw 29.

The next cut is performed following anoblique path from top to bottom and using asaw 10. The saw leaves a line mark as showedin Figure 2. The surgeon can then change thedirection of the saw to cut only about 5 mm fromthe bottom edge 31.

The manual separation of the bone fragmentsis then carried out by pushing downwards anddoing lateral movements along the ramus 10.The last step is to set both parts with mini platesand screws of titanium 10, 31, Figure 3.

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Figure 3: Fixation with titanium miniplates and screws 29.

4. SYSTEM DESCRIPTION

The proposed Virtual Osteotomy Simulator System (VOSS) for 3D osteotomy planning and training has the architecture

shown in Figure 4. The VOSS system comprises four main modules:

1. Visualization module, responsible of carrying out the graphic rendering of virtual objects and virtual environments.

2. Osteotomy module, to perform virtual osteotomies.

3. Manipulation module, to enable 3D free-form movement and manipulation of objects and surgical tools.

4. Data exportation module, to export any information regarding the osteotomy planning (e.g. STL files of models).

Figure 4: VOSS architecture.

The GUI of VOSS is shown in Fig. 5, which has been implemented using Phyton and Blender 2.59, in a PC with a 1.73 GHz

processor, 2.0GB of RAM and Windows XP. At the present, the VOSS systems allows for:

ü Virtual reality environment and real-time response.

ü 3D visualization of anatomical models and tools.

Fig. 3. Fixation with titanium miniplates andscrews 29.


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Figure 3: Fixation with titanium miniplates and screws 29.

4. SYSTEM DESCRIPTION

The proposed Virtual Osteotomy Simulator System (VOSS) for 3D osteotomy planning and training has the architecture

shown in Figure 4. The VOSS system comprises four main modules:

1. Visualization module, responsible of carrying out the graphic rendering of virtual objects and virtual environments.

2. Osteotomy module, to perform virtual osteotomies.

3. Manipulation module, to enable 3D free-form movement and manipulation of objects and surgical tools.

4. Data exportation module, to export any information regarding the osteotomy planning (e.g. STL files of models).

Figure 4: VOSS architecture.

The GUI of VOSS is shown in Fig. 5, which has been implemented using Phyton and Blender 2.59, in a PC with a 1.73 GHz

processor, 2.0GB of RAM and Windows XP. At the present, the VOSS systems allows for:

ü Virtual reality environment and real-time response.

ü 3D visualization of anatomical models and tools.

Fig. 4. VOSS architecture.

SYSTEM DESCRIPTION

The proposed Virtual Osteotomy SimulatorSystem (VOSS) for 3D osteotomy planning andtraining has the architecture shown in Figure 4.The VOSS system comprises four main modules:

1. Visualization module, responsible ofcarrying out the graphic rendering ofvirtual objects and virtual environments.

2. Osteotomy module, to perform virtualosteotomies.

3. Manipulation module, to enable 3D free-form movement and manipulation ofobjects and surgical tools.

4. Data exportation module, to exportany information regarding the osteotomyplanning (e.g. STL files of models).

The GUI of VOSS is shown in Fig. 5, whichhas been implemented using Phyton and Blender2.59, in a PC with a 1.73 GHz processor, 2.0GBof RAM and Windows XP. At the present, theVOSS systems allows for:

• Virtual reality environment and real-timeresponse.

• 3D visualization of anatomical models andtools.

• 3D free-form manipulation and interactionof cutting tool, bone, and bone fragments.

• Simulation of single and multipleosteotomies.

• Free-form cutting path osteotomy.

Figure 6a presents the methodology to definethe VR environment in the VOSS system. Thismethodology comprises the following steps inBlender:

• Create a scenario: The first stage is tocreate a scene in Blender to generate areal environment (lights, cameras, andbackground image).

• Load skull and jaw anatomical models:The bio-models are uploaded as STL or3DS files, and can be obtained fromreconstruction of medical images such asCT.


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ü 3D free-form manipulation and interaction of cutting tool, bone, and bone fragments.

ü Simulation of single and multiple osteotomies.

ü Free-form cutting path osteotomy.

Figure 5: Graphic user interface (GUI).

Figure 6a presents the methodology to define the VR environment in the VOSS system. This methodology comprises the

following steps in Blender:

• Create a scenario: The first stage is to create a scene in Blender to generate a real environment (lights, cameras, and

background image).

• Load skull and jaw anatomical models: The bio-models are uploaded as STL or 3DS files, and can be obtained from

reconstruction of medical images such as CT.

• Add texture to bone: In order to increase the realism of the VR environment, texture to the jaw bone is added by means

of an image. Since the skull is used only as reference and visual support, the texture is set as a transparency.

• Model cutting tools: Cutting tools (saw and drill) are modelled using the 3D modelling commands of Blender. They can

also be imported as STL or 3DS files.

• Add texture to tools: The tools (drill and saw) are texturized with image to reproduce their real appearance.

• Create sensors: Sensors are created to establish the keyboard and/or mouse buttons to control objects in the virtual

environment.

• Create controllers: Controllers are used to specify the next action to be performed after a sensor is activated.

• Create actuators: Actuators perform the movement or manipulation of the virtual objects according to the sensors.

Movements can be linear or rotational.

The movement or manipulation of virtual models within the platform can be made using the numeric keypad, alphanumeric

keypad or the computer mouse. These movements are defined by sensors, controllers and actuators. Figure 6b shows the

graphic interface whit all the methodology and manipulation elements.

Fig. 5. Graphic user interface (GUI).

8

(a) (b)

Figure 6: VR environment: a) methodology, b) implementation.

5. VIRTUAL OSTEOTOMY

The virtual osteotomy approach used in the VOSS corresponds to the BSSROM procedure, Figure 7. This procedure is

described in the following paragraphs.

(a) (b)

Figure 7: Virtual osteotomy: a) procedure, b) virtual model with mandibular deformation.

• Move the tool: Move the tool and place it at the point where the cut is needed. The user can select the tool to perform

the cut.

• Mesh edit: A Boolean operation is performed between the jaw (bone) and the tool models. The tool is subtracted from

the jaw. Virtual models are mesh models so they can be edited with Booleans operations.

• Evaluation: When the cut is performed with the sagittal saw, it is necessary to evaluate if the jaw was separated into two

parts. If the model is not separated yet, a new cut is performed with a new tool position.

• Separate volume: After the evaluation, the mesh model is then separated according to the volume occupied in the

scene. This will reduce the amount of data used in further processing.

Fig. 6. VR environment: a) methodology, b) implementation.


• Add texture to bone: In order to increasethe realism of the VR environment, textureto the jaw bone is added by means of animage. Since the skull is used only asreference and visual support, the textureis set as a transparency.

• Model cutting tools: Cutting tools (saw anddrill) are modelled using the 3D modellingcommands of Blender. They can also beimported as STL or 3DS files.

• Add texture to tools: The tools (drilland saw) are texturized with image toreproduce their real appearance.

• Create sensors: Sensors are created toestablish the keyboard and/or mousebuttons to control objects in the virtualenvironment.

• Create controllers: Controllers are used tospecify the next action to be performedafter a sensor is activated.

• Create actuators: Actuators performthe movement or manipulation of thevirtual objects according to the sensors.Movements can be linear or rotational.

The movement or manipulation of virtualmodels within the platform can be made usingthe numeric keypad, alphanumeric keypad orthe computer mouse. These movements aredefined by sensors, controllers and actuators.Figure 6b shows the graphic interface whit allthe methodology and manipulation elements.

VIRTUAL OSTEOTOMY

The virtual osteotomy approach used in theVOSS corresponds to the BSSROM procedure,Figure 7. This procedure is described in thefollowing paragraphs.

• Move the tool: Move the tool and place itat the point where the cut is needed. Theuser can select the tool to perform the cut.

• Mesh edit: A Boolean operation isperformed between the jaw (bone) andthe tool models. The tool is subtractedfrom the jaw. Virtual models are meshmodels so they can be edited with Booleansoperations.

8

(a) (b)

Figure 6: VR environment: a) methodology, b) implementation.

5. VIRTUAL OSTEOTOMY

The virtual osteotomy approach used in the VOSS corresponds to the BSSROM procedure, Figure 7. This procedure is

described in the following paragraphs.

(a) (b)

Figure 7: Virtual osteotomy: a) procedure, b) virtual model with mandibular deformation.

• Move the tool: Move the tool and place it at the point where the cut is needed. The user can select the tool to perform

the cut.

• Mesh edit: A Boolean operation is performed between the jaw (bone) and the tool models. The tool is subtracted from

the jaw. Virtual models are mesh models so they can be edited with Booleans operations.

• Evaluation: When the cut is performed with the sagittal saw, it is necessary to evaluate if the jaw was separated into two

parts. If the model is not separated yet, a new cut is performed with a new tool position.

• Separate volume: After the evaluation, the mesh model is then separated according to the volume occupied in the

scene. This will reduce the amount of data used in further processing.

Fig. 7. Virtual osteotomy: a) procedure, b) virtual model with mandibular deformation.


• Evaluation: When the cut is performedwith the sagittal saw, it is necessary toevaluate if the jaw was separated into twoparts. If the model is not separated yet,a new cut is performed with a new toolposition.

• Separate volume: After the evaluation, themesh model is then separated according tothe volume occupied in the scene. This willreduce the amount of data used in furtherprocessing.

• Clean the points: Many times some pointswould be out of the main jaw mesh, leadingto additional volumes. It is importantto eliminate those volumes because thealgorithm only moves the two jaw mainfragments (Jaw 1 and Jaw 2).

• Reposition of the jaw: Once the jaw hasbeen separated into two parts, the largestpart (Jaw 1) is moved or manipulated toits final position at the other part (Jaw 2).

• Join the model: The final step is to alignand join the two parts of the jaw.

The procedure may be also performed tothe other side of the jaw bone. Normallythe BSSROM procedure requires the cutting ofbooth jaw ramus. In this case the previousmethodology is then repeated to the other jawside.

RESULTS AND DISCUSSION

To evaluate the feasibility of the VOSS, acase study is now developed. The BSSROMprocedure begins by selecting a cutting tool andplacing it at the position where the first cut ismean to be made, Figure 8. Once the tool ispositioned, the cut is performed and it can berepeated as many times as necessary to make alongitudinal cut along the jaw.

The manipulation and location of the toolcan be made in a free-form way, i.e. theuser can freely move the tool in any 3D pathwhile performing the cut. Figure 9a shows thesimulation of a vertical cut path using a drill,

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• Clean the points: Many times some points would be out of the main jaw mesh, leading to additional volumes. It is

important to eliminate those volumes because the algorithm only moves the two jaw main fragments (Jaw 1 and Jaw 2).

• Reposition of the jaw: Once the jaw has been separated into two parts, the largest part (Jaw 1) is moved or manipulated

to its final position at the other part (Jaw 2).

• Join the model: The final step is to align and join the two parts of the jaw.

The procedure may be also performed to the other side of the jaw bone. Normally the BSSROM procedure requires the

cutting of booth jaw ramus. In this case the previous methodology is then repeated to the other jaw side.

6. RESULTS AND DISCUSSION

To evaluate the feasibility of the VOSS, a case study is now developed. The BSSROM procedure begins by selecting a

cutting tool and placing it at the position where the first cut is mean to be made, Figure 8. Once the tool is positioned, the cut

is performed and it can be repeated as many times as necessary to make a longitudinal cut along the jaw.

Figure 8: Initial positioning of the tool.

The manipulation and location of the tool can be made in a free-form way, i.e. the user can freely move the tool in any 3D

path while performing the cut. Figure 9a shows the simulation of a vertical cut path using a drill, while Figure 9b shows the cut

using a saggital saw to separate the jaw bone.

(a) (b)

Figure 9: Available cutting process: a) drill b) sagittal saw

Fig. 8. Initial positioning of the tool.

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(a) (b)


9
















(a) (b)


Fig. 9. Available cutting process: a) drill b)sagittal saw.


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As in the real procedure, the jaw can be separated into two parts which can then be moved or manipulated independently.

Figure 10 shows the bone fragments after the separation.

Figure 10: New position from jaw 1 to jaw 2.

After the manipulation and relocation of the jaw parts, a Boolean operation can be carried out to join the jaw parts. Figure 11

shows the last movement and final relocation of the mandible.

Figure 11: Final step in the virtual osteotomy.

The proposed VOSS system allowed the 3D rendering of anatomical models corresponding to an upper maxillary and a jaw.

Different textures, lighting and visual properties can be used to increase the realism level. It has been proved that 3D virtual

osteotomy procedures can be performed using the proposed system. The time performance of the cutting procedure depends

on the size of the anatomical models (in particular on the number of elements in the mesh); the average time to perform a cut

varies from 250 to 300 milliseconds, for a standard jaw and tool size. Anatomical models can be reconstructed from CT

images (DICOM) and be imported into the VOSS system as STL files.

7. CONCLUSIONS

The development of a virtual simulator for planning a Bilateral Sagittal Split Osteotomy Ramus Mandibular surgery has been

presented in this paper. The system has been developed using open-source software and without sacrificing the level of

realism. The results of the implementation and evaluation have demonstrated that it is possible to perform virtual osteotomies

using the proposed system. Future work comprises the incorporation of haptic devices to manipulate tools and virtual objects

in the VOSS system.

ACKNOWLEDGMENTS

The authors would like to acknowledge the financial support from CONACYT (National Science and Technology Council),

research grant CB-2010-01-154430. They also thank to UASLP, HWU and ITC for the support provided to this research work.

Jaw1

Jaw2

position

Fig. 10. New position from jaw 1 to jaw 2.

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As in the real procedure, the jaw can be separated into two parts which can then be moved or manipulated independently.

Figure 10 shows the bone fragments after the separation.

Figure 10: New position from jaw 1 to jaw 2.

After the manipulation and relocation of the jaw parts, a Boolean operation can be carried out to join the jaw parts. Figure 11

shows the last movement and final relocation of the mandible.

Figure 11: Final step in the virtual osteotomy.

The proposed VOSS system allowed the 3D rendering of anatomical models corresponding to an upper maxillary and a jaw.

Different textures, lighting and visual properties can be used to increase the realism level. It has been proved that 3D virtual

osteotomy procedures can be performed using the proposed system. The time performance of the cutting procedure depends

on the size of the anatomical models (in particular on the number of elements in the mesh); the average time to perform a cut

varies from 250 to 300 milliseconds, for a standard jaw and tool size. Anatomical models can be reconstructed from CT

images (DICOM) and be imported into the VOSS system as STL files.

7. CONCLUSIONS

The development of a virtual simulator for planning a Bilateral Sagittal Split Osteotomy Ramus Mandibular surgery has been

presented in this paper. The system has been developed using open-source software and without sacrificing the level of

realism. The results of the implementation and evaluation have demonstrated that it is possible to perform virtual osteotomies

using the proposed system. Future work comprises the incorporation of haptic devices to manipulate tools and virtual objects

in the VOSS system.

ACKNOWLEDGMENTS

The authors would like to acknowledge the financial support from CONACYT (National Science and Technology Council),

research grant CB-2010-01-154430. They also thank to UASLP, HWU and ITC for the support provided to this research work.

Jaw1

Jaw2

position

Fig. 11. Final step in the virtual osteotomy.

while Figure 9b shows the cut using a saggitalsaw to separate the jaw bone.

As in the real procedure, the jaw can beseparated into two parts which can then bemoved or manipulated independently. Figure 10shows the bone fragments after the separation.

After the manipulation and relocation of thejaw parts, a Boolean operation can be carried outto join the jaw parts. Figure 11 shows the lastmovement and final relocation of the mandible.

The proposed VOSS system allowed the 3Drendering of anatomical models corresponding toan upper maxillary and a jaw. Different textures,lighting and visual properties can be used toincrease the realism level. It has been provedthat 3D virtual osteotomy procedures can beperformed using the proposed system. The timeperformance of the cutting procedure depends onthe size of the anatomical models (in particularon the number of elements in the mesh); theaverage time to perform a cut varies from 250to 300 milliseconds, for a standard jaw and toolsize. Anatomical models can be reconstructedfrom CT images (DICOM) and be imported intothe VOSS system as STL files.

CONCLUSIONS

The development of a virtual simulator forplanning a Bilateral Sagittal Split OsteotomyRamus Mandibular surgery has been presentedin this paper. The system has beendeveloped using open-source software andwithout sacrificing the level of realism. Theresults of the implementation and evaluationhave demonstrated that it is possible to performvirtual osteotomies using the proposed system.Future work comprises the incorporation ofhaptic devices to manipulate tools and virtualobjects in the VOSS system.

ACKNOWLEDGMENTS

The authors would like to acknowledge thefinancial support from CONACYT (NationalScience and Technology Council), research grantCB-2010-01-154430. They also thank to UASLP,HWU and ITC for the support provided to thisresearch work.

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